1. Field of the Invention
The present invention relates to an optical information recording-reproducing apparatus, and in particular to such apparatus employing a card-shaped optical information recording medium.
In the present invention, the optical information recording-reproducing apparatus shall include an apparatus for recording information on a medium as mentioned above, an apparatus for reproducing information recorded on such medium, and an apparatus for recording and reproduction of information.
2. Description of the Prior Art
For the purpose of optical recording and reproduction of information there are already known disk-, card- and tape-shaped media. Among these, an optical recording medium formed as a card (hereinafter called optical card) is considered to have a large demand as a small, light and portable recording medium of a large capacity.
In such optical card, information is recorded as a row of optically detectable record pits by scanning a recording track, determined in advance on the optical card, with a light beam which is modulated according to the information to be recorded and focused to a small spot. In such operation, in order to exactly record the information without failures such as crossing of the rows of record pits, there has been required automatic tracking for controlling the irradiating position of the light beam in a direction perpendicular to the scanning direction. Also there has been conducted automatic focusing for precisely focusing the light beam onto the optical card. Consequently, in order to obtain a tracking signal and a focusing signal from the recording track, the modulated light beam has been designed to have a power just below the level required for information recording even at the minimum value. On the other hand, the reproduction of recorded information has been conducted by scanning the row of record pits with a light beam of a constant power not enough for information recording onto the optical card.
In the information recording-reproducing means for optical card as explained above, the scanning with the light beam is achieved by relative movement of the optical card and the light beam at information recording or reproduction. As the recording tracks are formed as plural linear lines on the optical card, the scanning is conducted intermittently, inevitably involving standstill states of the light beam.
If the light beam remains standstill in such conventional apparatus, erroneous signal recording may take place by the accumulation of energy even with the light beam of the aforementioned level not enough for information recording. Such erroneous signal is also detected by the light beam, causing serious trouble, for example, in track access, an operation of moving the light beam to a desired track position.